Sunday, May 11, 2014

Improved Ethanol Yield by Cellulosic Process

Subtitle: Genetic Engineering Provides 160 Percent Ethanol Yield Increase

A recent paper by Van Acker, R. et al. in Proceedings of the National Academy of Sciences U.S.A., Volume 111, Issue 2, p.845-850 (2014) see link , describes an improved means to create ethanol from cellulose.  The researchers genetically modified the lignin in poplar trees so that more of the cellulose converts to ethanol compared to unmodified trees.   The increased yield varied, but some trees showed a 160 percent increase in yield.  That is somewhat reduced by the reduction in mass of the trees.   Clearly, more research will be needed to sort out the best yielding trees from the worst, and to define the economics. 

Poplar trees are fast-growing, approximately one foot four to eight feet per year, and grow on marginal land that is not suitable for crops. [see link for USDA information on Poplar trees]
Poplar trees (Populus alba) - image: USDA
.  Ethanol from trees grown on such marginal land has been possible for some time, but not yet economical.  The problem, or one of the problems, has been the low ethanol yields from natural lignin.  It can be done, but the yields are low and the costs per unit of ethanol are high.   Marginal land for ethanol-producing biomass is preferred so that crops can be used for food, not fuel.  The food crops price will decrease, since the market will be only food and not food plus fuel.  Lower food prices are a good thing, especially if one is poor or on a limited income. 

The research showed that it is possible to genetically modify the lignin rather than improve the process on natural lignin.    This research may be a watershed moment in science, of which there have been very few in all of history.   The ability to grow trees on hillsides, and in poor soils has long been with us.  But, having those trees converted economically into ethanol, a transportation fuel that substitutes for gasoline, has been a difficult problem.  

From the paper's Abstract: "Lignin is one of the main factors determining recalcitrance to enzymatic processing of lignocellulosic biomass. Poplars (Populus tremula x Populus alba) down-regulated for cinnamoyl-CoA reductase (CCR), the enzyme catalyzing the first step in the monolignol-specific branch of the lignin biosynthetic pathway, were grown in field trials in Belgium and France under short-rotation coppice culture. Wood samples were classified according to the intensity of the red xylem coloration typically associated with CCR down-regulation. Saccharification assays under different pretreatment conditions (none, two alkaline, and one acid pretreatment) and simultaneous saccharification and fermentation assays showed that wood from the most affected transgenic trees had up to 161% increased ethanol yield. Fermentations of combined material from the complete set of 20-mo-old CCR–down-regulated trees, including bark and less efficiently down-regulated trees, still yielded ∼20% more ethanol on a weight basis. However, strong down-regulation of CCR also affected biomass yield. We conclude that CCR down-regulation may become a successful strategy to improve biomass processing if the variability in down-regulation and the yield penalty can be overcome."

This is the type of scientific advance that is worth pursuing for the long-term welfare.  The US presently mandates that all gasoline sales include ten percent by volume ethanol, with a 15 percent provision also in some instances.  However, the ethanol is currently made from corn fermentation.  The gasoline sold in the US is approximately 9 million barrels per day, or 136 billion gallons per year.  The ethanol, at 10 percent, is then 13 billion gallons per year.  Replacing that ethanol from corn with ethanol from cellulose would reduce corn prices, and the prices of many foods that depend on corn price.  

This is a research effort that bears watching. 

Roger E. Sowell, Esq. 
Marina del Rey, California

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